The present invention relates to a method of fabricating semiconductor devices in which elements are formed in a semiconductor layer formed on a single crystalline insulation substrate.
The semiconductor device of this type, known as an SOS (silicon on sapphire), for example, has generally been fabricated using a silicon layer epitaxially grown on a single crystal sapphire substrate. Since this method employs the epitaxial growing process for forming the silicon layer, however, it takes a long time for the silicon layer formation and is a low productivity process. The epitaxial growing process is continued at high temperature of about 1,000.degree. C. for a long time. In the course of this process, the auto-doping of the aluminum from the sapphire substrate takes place, resulting in remarkable deterioration of the element characteristics.
In this type semiconductor device, there is known a method for insulating an element in which the silicon thin layer portion (i.e. called the field region) except for the element region is etched away thereby isolating the elements individually. In order to avoid the adverse effect of the end face of the isolated silicon region, it is desirable to employ an element insulating method in which the field region is selectively oxidized to form an oxide film. Also in this selective insulating method, the auto-doping takes place like the previous case. The result is that the oxidizing temperature is limited and much time is required for the oxidizing process.